This relates to an opposing spring suspension including a resilient tension member between the chassis and each wheel axle support. More particularly, each resilient tension member uses the unsprung weight of the wheel/axle to help resist the rebound travel of the suspension and so reduce the chassis side sway and pitching forward and aft due to hard acceleration and deceleration.
In the past ten years the numbers of sport utility vehicles xe2x80x9cSUVxe2x80x9d and pickup trucks have increased dramatically to the point where those vehicles are more popular than the millions of passenger cars on the road. The SUV and trucks inherently have a higher center of gravity than normal passenger cars due to the need for higher ground clearance for bad weather travel (snow and ice), off-road use and/or for pickup truck payloads. Typically these vehicles have a higher center of gravity and so a greater propensity to sway or even rollover during abrupt lane changes and evasive steering maneuvers than the lower normal passenger cars.
One important arrangement of all these vehicles is the method of suspension used. Except for the use of hydraulic shock absorber damping resistance to rebound, all suspension have the vehicle chassis and body load supported on the vehicle axles with various types of springs that resist primarily load and jounce of each wheel axle. All existing coil springs, leaf springs, air springs, torsion bars or rubber blocks suspensions have no provision for control of the rebound forces of inertia and gravity negative suspension loads. Particularly, those rebound loads occurring at the inside wheel during hard cornering or if a wheel drops into a pot hole. Typically, changes in suspension loads while driving straight along a road are caused generally by reactions to bumps, pot holes, and roughness encountered by the vehicle wheels during their interaction with the road surface. Thus the suspension springs and associated shock absorbers quell the harshness and movements being transmitted to the body and chassis.
The sway or side to side rolling motions that vehicles experience due to cornering forces, also cause vehicle springs to be loaded or unloaded, depending which way the vehicle is rolling during cornering. Many vehicles have an anti-sway/roll bar installed to help the vehicle body resist the rolling actions. These devices help somewhat the vehicle resist roll but only as it relates to the body lean, because they are fixed to the sprung mass and leaning with the body. Thus, they actually reduce the load on the unloaded side of the vehicle. They use the body as a structure to support the torsion bar of the anti sway system transferring wheel jounce motion across to the opposite side. The disclosure herein will obviate the need for anti-sway bars saving the cost of providing and installing them. Shock absorbers only dampen the bouncing movement of the vehicle wheels and suspension caused by the reaction to road surface, cornering and braking. Thus, the rate of sway may be affected to a minor degree.
The transitory effects of body roll during cornering compress the springs on the side of the vehicle following the outside of the turn due to increased transfer weight to that side. Meanwhile the springs on the side of the vehicle, following the inside of the turn, unload extending toward their free position using the axle as a location for inducing lift of the sprung weight on that side resulting in increased body roll. Roll or sway during sudden cornering or evasive maneuvers rotates the vehicle and its center of gravity xe2x80x9cCGxe2x80x9d around the Roll Center axis. The Roll Center axis is a function of the particular vehicles suspension geometry. Roll or sway is increased if the CG is raised as in a SUV, four-wheel drive vehicle or truck.
A sudden turn opposite the direction of vehicle travel can cause momentum to continue the sway of the vehicle forcing its CG to move laterally past its maximum upright position, and so the vehicle continues on rolling and overturns. U.S. Pat. No. 2,160,541 has a paired spring suspension connected in series to only support load and jounce with the added spring coupled in line with the main spring for increasing the effective spring constant at the extremes of suspension travel. The techniques disclosed in the various embodiments of ""541 are in the nature of an overload spring that engages and changes the spring constant at the extremes of wheel travel. There is no spring in ""541 connected to specifically resist rebound forces due to diverging motion of the sprung weight to unsprung weight. The disclosure of ""541 specifically states that the higher spring constant results in less flex (on page 2 column 1 at lines 6 to 8), xe2x80x9c . . . which opposes any tendency of the vehicle to overturn laterally when negotiating a turn.xe2x80x9d In each embodiment of ""541 the springs act in unison to control primarily load and jounce and there is no teaching of a particular connection to directly apply rebound reaction of unsprung weight to one of the springs. The graph in ""541 showing wheel travel verses spring forces verifies these conclusions. U.S. Pat. No. 5,263,695 discloses a refinement of the ""541 teaching that includes a shock absorber for damping motion and an elastic block to ameliorate the transition between first and second springs for carrying the load. In addition to many disclosures in ""695 of prior paired spring configurations there is a specific explanation in column 5, lines 1 through 5 as follows:
xe2x80x9cThe suspension according to the invention produces a comfort level which is higher the more the transition from one stiffness to the other takes place progressively (see the patents cited in the state of the art).xe2x80x9d
The state of the art referred to includes prior patents of the same inventor and the acknowledgements of those prior patents clearly identifies the teachings as merely two springs of different stiffness in series. Even in FIG. 7 of ""695 the springs are concentrically mounted but act in series, see column 4, lines 8 through 12. At best the structures for multiple springs shown in these patents have differing spring rates to give an allegedly more comfortable ride.
No existing suspension system suspends the chassis and body between opposing springs to counter load and jounce and reaction and rebound along different portions of the axle and wheel travel. An opposing spring suspension can have little effect on the ride stiffness but stabilizes cornering and evasive maneuvering sway by helping the vehicle to resist roll while maintaining the general ride quality.
A vehicle opposed spring system is preferably placed between a chassis having a sprung weight and a plurality of wheel axle supports each carrying and a portion of an unsprung weight. Sprung weight and unsprung weight are defined at the web site, inner auto.com as follows:
xe2x80x9cSprungxe2x80x9d weight is a term used to describe the parts of a vehicle that are supported by the front and rear springs. They suspend the vehicle""s frame, body, engine, and the power train above the wheels. These are quite heavy assemblies. The xe2x80x9cunsprungxe2x80x9d weight includes wheels and tires, brake assemblies, the rear axle assembly, and other structural members not supported by the springs.xe2x80x9d
The opposed spring system may include a resilient load bolster mounted between the chassis and the wheel axle support to carry when preloaded the chassis at a preset ride height relative to the wheel axle support. A resilient member affixed between each wheel axle support and the chassis preferably exerts increasing force there between as a function of the amount of motion of the unsprung weight relative to the chassis. The resilient member mounted to move between the chassis and the wheel axle support. The resilient member most preferably applies increasingly less force to the resilient load bolster during jounce beyond the preloaded preset ride height of the resilient load bolster and the resilient member increasingly resists the motion of unsprung weight on the wheel axle support.
The resilient member has a free length of travel that operates in cooperation with the resilient load bolster jounce deflection so the free length of travel and the jounce deflection overlap when the resilient member moves between the chassis and the wheel axle support. The chassis preferably has a substantially rectangular footprint having four wheels disposed generally to carry the corners thereof with each comer having its wheel axle support moveably carried by its resilient load bolster and its resilient member to resist jounce and rebound, respectively. A shock absorber can be located between and affixed to the chassis for each wheel axle support for damping the jounce and rebound motions there between progressively decreasing the frequency of the wheel axle support motion.
The resilient member is most preferred to be a coil spring having its free length of travel preloaded with tension sufficient to maintain its connection between the chassis and the wheel axle support even when the resilient load bolster is compressed to its maximum load capacity. The resilient member alternatively might be an elastic member having its free length of travel stretched sufficiently between the chassis and the wheel axle support to attach thereto even when the resilient load bolster is compressed to its maximum load capacity. The resilient member could be a torsion spring with torque preloaded sufficiently between the chassis and the wheel axle support to maintain connection there between even when the resilient load bolster is compressed to its maximum load capacity.
The resilient load bolster preferably has an elastic constant of K to carry sprung weight on the wheel axle support and the resilient member has an elastic constant KT for resisting the rebound motion of the sprung weight over the wheel axle support. The relationship of the elastic constant of K to carry sprung weight for jounce and the elastic constant KT for resisting the rebound motion of the sprung weight is a function of the amount of roll resistance.
A preferred vehicle opposed spring system is placed between a chassis wherein a sprung weight and a plurality of wheel axle supports each carrying a portion of an unsprung weight. The opposed spring system preferably has a coil load spring mounted between the chassis and each wheel axle support to carry when preloaded the chassis at a preset ride height relative to each wheel axle support. A coil tension spring is most preferably affixed between each wheel axle support and the chassis exerts increasing force thereat as a function of the amount of rebound motion of the sprung weight. The coil tension spring mounts relative to the coil load spring for stretching between the chassis and the wheel axle support. The coil tension spring applies increasingly less rebound force to the coil load spring during jounce through and beyond the preset ride height of the coil load spring as each coil tension spring resists the rebound motion of sprung weight at each wheel axle support.
Each coil load spring is coaxial with its respective load spring axis disposed approximately normal to the chassis and each wheel axle support. Each coil load spring has a concentric volume defined thereby and located there within for disposition of its coil tension spring there within its concentric volume for movement therein without binding with the coil load spring during jounce and rebound.
Each coil load spring may alternatively be coaxial with a load spring axis disposed approximately normal to the chassis and each wheel axle support. Each coil tension spring is then preferably spaced apart from the coil load spring and is disposed along a tension spring axis generally parallel to the load spring axis of each coil load spring. Each coil tension spring may move relative to its respective coil load spring during jounce and rebound.
An alternative may have a plurality of coil control springs affixed between each wheel axle support and the chassis for exerting increasing force thereat as a function of the amount of rebound motion of the sprung weight relative of the chassis. Each coil control spring can oppose its respective coil load spring applying increasingly less rebound force thereto during jounce through and beyond the preset ride height of the coil load spring as each respective coil control spring resists the rebound motion of sprung weight over its respective wheel axle support. A path is preferably defined by each of the lines between the chassis and the wheel axle support. Along each path each coil load spring and its respective coil control spring jounce and rebound. The coil control spring has preferably has a free length of travel that cooperates with the coil load spring jounce deflection along the path so the free length of travel along the path and the jounce deflection along the path overlap.
Each wheel axle support may have a rod fixed to the chassis extending along the line for supporting a suspension platform. Each suspension platform is most preferably disposed in compression and for reciprocation along the path with and between the coil load spring and the coil control spring during jounce and rebound and the suspension platform affixed to the wheel axle support.
The opposing spring suspension preferably has two opposing springs that seek to keep the vehicle stabilized in a predetermined sprung position of height relative to the wheel axle system of the vehicle. This sprung position is preferably arrived at by using a compression spring of a known rate per inch in series with and a tension or compression spring also of a known rate per inch, that through their opposition, position chassis body at a neutral location arrived at as the result of the sum of the opposing forces. A simpler illustration of what happens can be understood by imagining a paper clip suspended between two extended rubber bands stretched in opposite directions tethering the clip between their ends. Motion of the paper clip toward one rubber band end would shorten that rubber band and lengthen the other. Releasing the tension on the paper clip returns it to its former location between the two stretched bands. This simple demonstration shows how the vehicle has the capability to quickly return to a constant ride height position relative to the ground. This capability should vastly reduce the tasks to be performed by the standard equipment shock absorbers of the vehicle and in fact increase shock life expectancy dramatically, due mainly to reduced use and associated heat.